Among conventional turbidity sensors, there is one which includes: a cylindrical measuring cell for accommodating a liquid sample; a light source; a transmitted light detector and scattered light detector; and a sensor accommodating part for accommodating the light source, transmitted light detector, and scattered light detector, wherein the light source, transmitted light detector, and scattered light detector are provided outside the measuring cell, as disclosed in Patent Literature 1. Both end portions in an axial direction of the measuring cell are fixed to the sensor accommodating part via a sealing member. Then, the light source, transmitted light detector, and scattered light detector are fixed in a space which is formed between the sensor accommodating part and the measuring cell.
Further, the measuring cell includes a first transparent window corresponding to the light source, a second transparent window corresponding to the transmitted light detector and a third transparent window corresponding to the scattered light detector. The first, second, and third transparent windows are formed of a material having an optical transparency. The main body portions other than the first, second, and third transparent windows are formed of a material having a light-shielding property.
However, in this turbidity sensor, since the light source, transmitted light detector, and scattered light detector are accommodated in a space formed between the sensor accommodating part and the measuring cell, the liquid sample infiltrates into the space due to factors such as deterioration of the sealing member in both end portions in the axial direction of the measuring cell, and this results in events such as a failure of the light source, transmitted light detector, and scattered light detector. Moreover, it is necessary to assemble the measuring cell and sensor holding part via the sealing member, and therefore there is also a problem that not only does assembly become complicated, but also the turbidimeter is then easily damaged by an external impact.
Further, since the respective transparent windows and the main body portions other than the respective transparent windows in the measuring cell are composed of different materials, it is necessary to ensure sufficient sealing of these transparent windows and main body portions, and therefore a problem may likely arise that the sealing is degraded during a long period of use. Also, it is necessary that the respective transparent windows are fitted to the main body portion of the measuring cell and sufficient sealing is ensured. Therefore, not only does assembly become complicated, but there is also a concern that the transparent windows may be shifted by an impact from the outside.